1. Field of Invention
This invention relates to polymer films. More particularly, this invention relates to ultrathin polymethylmethacrylate polymer films and their production.
2. Prior Art
The preparation of polymethylmethacrylate and methyl methacrylate polymer, free-standing films on a liquid support, such as water, is known. However, most of the prior art films have thicknesses that are greater than 500 angstroms and accordingly cannot be classified as "ultrathin" films. For example, U.S. Pat. Nos. 2,537,969, and 2,537,970 disclose methylmethacrylate sheets having a thickness of about 1/8 inch prepared on an aqueous salt solution support. In U.S. Pat. No. 2,607,081, sheets having a thickness of about 1/8 inch are prepared by casting a syrup containing some polymethylmethacrylate but mostly monomeric methylmethacrylate on an aqueous salt solution.
In U.S. Pat. No. 2,760,233, a process is disclosed for preparing curved polymer sheets from methacrylic acid ester polymers. However, no specific solvent mixtures and ratios suitable for casting ultrathin, pinhole-free, polymethylmethacrylate films are disclosed nor are any film thicknesses provided.
U.S. Pat. No. 3,551,244 discloses a process for preparing on a water surface films having a thickness between 0.05 and 5.0 microns (i.e. between 500 and 50,000 angstroms). The patent discloses that certain esters, such as ethyl acetate, are suitable casting solvents and states that polymethylmethacrylate films can be prepared. However, no specific solvent mixtures and ratios suitable for casting pinhole-free, polymethylmethacrylate films with thicknesses less than 400 angstroms are disclosed.
U.S. Pat. No. 3,767,737 discloses a method for producing allegedly nonporous, alkyl methacrylate polymer membranes having thicknesses between 0.005 and 0.05 mils on a support liquid. In the only relevant example, it is unclear whether polymethylmethacrylate is employed alone or in combination with other polymers to prepare a film. Nevertheless, specific mixtures of solvents and appropriate solvent ratios for preparing pinhole-free, polymethylmethacrylate films having thickness of 400 angstroms or less are not disclosed.
U.S. Pat. Nos. 4,155,793, 4,279,855 and 4,374,891 disclose processes for preparing substantially void-free, ultrathin, permeable polymeric membranes having a thickness of 500 angstroms or less. Alkyl methacrylate polymers are asserted to be suitable for use in the disclosed process. However, only films prepared from organopolysiloxane-polycarbonate interpolymers mixed with polyphenylene oxide are disclosed in the examples. Polymethylmethacrylate filmes are not disclosed nor are suitable solvent mixtures and ratios for casting polymethylmethacrylate films having thicknesses of 400 angstroms or less.
Other patents, such as U.S. Pat. Nos. 2,631,334, 2,689,187, and 4,393,113, also disclose ultrathin polymeric films. However, no polymethylmethacrylate films are disclosed.
In the prior art, the preparation of monolayer polymethylmethacrylate films, which are one molecule thick, by depositing polymethylmethacrylate solutions on water is known. (See for example "On-line Diagnostics for Langmuir-Blodgett Film Growth," by Stephen Kowel, et al., Thin Solid Films, 132 (1986)). Such films are commonly called Langmuir-Blodgett films. However, such films are not free-standing films and are generally removed from the casting surface by affixing them to a substrate, such as glass.
In the prior art, pinhole-free, polymethylmethacrylate, free-standing films with thickness of less than 400 angstroms generally have not been cast. Usually, prior art films with thicknesses of less than 400 angstroms that are cast have holes and other macroscopic defects.
Therefore, it is an object of this invention to prepare ultrathin polymethylmethacrylate polymer films.
It is a further object of this invention to prepare pinhole-free, polymethylmethacrylate polymeric films.
It is also an object of this invention to prepare free-standing, polymethylmethacrylate films having thicknesses of 400 angstroms or less.
These and other objects are obtained by the products and process of the present invention.